Rubber-Tired Gantry (“RTG”) cranes are widely used in port facilities to move cargo, especially large cargo containers. These cranes typically can lift and transport loads weighing in the range of about 10,000 kilograms to about 50,000 kilograms. RTG cranes are typically powered by a diesel engine whose mechanical energy is converted to DC electrical power which is then used to drive AC lift and propulsion drive motors. The diesel engine is typically oversized to provide peak power bursts and prevent excessive voltage drop when lifting. These engines are typically run at constant speed for frequency control and so are not maximized for fuel efficiency. In typical service, the RTG crane has a duty cycle with a high idle content which reduces overall fuel efficiency and increases unwanted emissions.
Overhead cranes are similar to RTG cranes except they follow a predetermined track. These cranes typically can lift and transport loads weighing in the range of about 10,000 kilograms to about 120,000 kilograms. References to RTG cranes hereafter are understood to include overhead cranes as well.
The duty cycle of an RTG crane is similar in many ways to a yard switching locomotive. One of the present inventors, Donnelly, has disclosed the use of a battery-dominant hybrid locomotive in U.S. Pat. No. 6,308,639 which is designed to reduce emissions and fuel consumption for locomotives used in yard switching and other industrial applications which have duty cycles similar to that of an RTG crane. U.S. Pat. No. 6,308,639 is incorporated herein by reference.
In U.S. patent application Ser. No. 11/200,881 filed Aug. 19, 2005 entitled “Locomotive Power Train Architecture”, now U.S. Pat. No. 7,304,445 Donnelly et al. have further disclosed a general electrical architecture for locomotives based on plurality of power sources, fuel and drive train combinations. The power sources may be any combination of engines, fuel cells, energy storage and regenerative braking. This general electrical propulsion architecture is also applicable to RTG cranes. U.S. patent application Ser. No. 11/200,881 is also incorporated herein by reference.
Donnelly et al. have further disclosed a system for controlling a dynamic and regenerative braking system for a hybrid locomotive which employs a control strategy for orchestrating the flow of power amongst the prime mover, the energy storage system and the regenerative braking system in a U.S. patent application Ser. No. 11/200,879 filed Aug. 9, 2005 entitled “Regenerative Braking Methods for a Hybrid Locomotive” which is also incorporated herein by reference.
In addition, Donnelly et al. have disclosed a method of dynamic braking of a locomotive which is operable down to very low speeds in a U.S. patent application filed Apr. 19, 2006 entitled “Dynamic Braking for a Hybrid Locomotive” which is also incorporated herein by reference.
U.S. Pat. No. 6,688,481 entitled “Mobile Crane” discloses a hybrid mobile crane wherein “at least one electric motor propels the undercarriage in an operating direction and is supplied with electric power for driving and crane operations by a power supply unit which is connected to the at least one electric motor by a cabling and configured as a diesel-electric drive, or a battery, or a multi-system drive formed by a combination of a diesel-electric drive with a battery, or a fuel-cell system.” When electric power is supplied by the multi-system drive configuration, propulsion and lifting operations are carried out predominantly by the diesel-electric drive and only temporarily by the battery. When operating in an enclosed environment, the crane may be operated using battery power only where battery obtains most of its energy from power outlet of the electric mains so that the crane operation can be carried out without emission of pollutants.
This type of crane typically has superstructure rotatably mounted on the undercarriage for supporting a counterweight, a slewable telescopic boom assembly and an operator's cab. U.S. Pat. No. 6,688,481 discloses a hybrid version of this mobile crane which is intended to overcome two shortcomings of the non-hybrid mobile crane. These are (1) the restriction on the freedom of placement that all power components and (2) operations that inevitably result in engine-torque jumps and transient operating states that are determinative for the toxic constituents contained in the exhaust gas. The mobile crane of U.S. Pat. No. 6,688,481 does not indicate that it can utilize a large battery pack such as would be necessary to store a large amount of energy nor provide significant additional power surge capability when needed. Further, the mobile crane of U.S. Pat. No. 6,688,481 does not include a regenerative braking capability and so does not maximize fuel efficiency. The mobile crane of U.S. Pat. No. 6,688,481 includes the possibility of using fuel cells but appears to use fuel cells in place of a battery pack, not as a possible prime power source.
Other prior art documents disclose the use of energy storage units for load-lifting devices. U.S. Pat. No. 4,456,097 by Salihi discloses a battery-powered elevator system. In this system, the battery is charged by a battery charger and is regenerated by a polyphase motor. However, the charge of the battery is mainly supplied externally and is separate from the internal power architecture of the elevator.
U.S. Pat. No. 6,732,838 by Okada et al. discloses an AC. elevator including a power source with a rechargeable battery. However, the battery is not directly connected to the DC power bus of the system and requires a charge control element, while being restricted to AC motors.
U.S. Pat. Nos. 5,936,375 and 7,165,654 by Enoki and Takehara et al. respectively disclose a method for energy storage and recovery for load hoisting equipment. These prior art documents mention that combination battery and generator energy storage systems have been utilized to accomplish this result in the past, and theoretically they are very effective. However, these documents state that, according to their knowledge, the battery component imposes numerous problems such as: small electrical capacity, electrical inefficiency, large physical battery volume, heavy weight, and short battery life, whereby such a system is not currently a viable way to accomplish energy storage utilizing even state-of-the-art battery technology. The authors then suggest methods of using flywheel and/or capacitor systems for storing energy.
There thus remains a need for a load-lifting apparatus that utilizes a common DC bus architecture that can be operated on any type of prime power supply and recoup and store a significant amount of energy through regenerative braking primarily when the load is being lowered. There is also a need for a power architecture that would allow an efficient use of battery power storage systems for load-lifting applications.